1. Field of the Invention
The present invention generally relates to a vehicle seat. More specifically, the present invention relates to a seatback for a vehicle seat, which can mitigate an impact to an occupant at the time of a collision from rear.
2. Background Information
Japanese Laid-Open Patent Application H7-291005 shows a connection member is provided in a connecting portion that connects a seatback frame and a plurality of cushion members. The seatback frame supports a headrest. The cushion members are S springs that are installed in a seatback. The connecting members move in a rearward direction when a load greater than a predetermined amount is applied to the connecting members. When the occupant is pushed against the cushion members as a reaction to the impact of the collision of the vehicle, and accordingly the load applied to the cushion members reaches a predetermined value, the connecting members that are on both sides of the cushion member being pushed extend in the rearward direction. In this manner, the posture of the occupant is maintained, while making the headrest receive the head of the occupant securely.
However, the shape of seatback and the distribution of the rigidity of seatback generally need to be determined taking into consideration ease of driving operation, comfort to the occupant, and ability to mitigate fatigue. Particularly, in order to allow the occupant to maintain a proper sitting posture effectively, the seatback structure has to support the lumbar vertebrae. Thus, this type of seatback is designed to form a high rigidity part in the lumbar support area.
At the time of collision of the vehicle, the occupant moves in the rearward direction relative to the vehicle body and the seat due to the inertial force. In the above structure, the connecting portion between the cushion members such as S springs and the seat frame moves in the rearward direction upon receiving a uniform predetermined load. In such structure, when a great load is applied to the lumbar support area, the S spring behind the lumbar support area moves rearward, while other S springs do not move. As a result, the S springs behind the thoracic vertebrae, for instance, do not move rearward until the load in the thoracic support area becomes great enough.
Furthermore, if the occupant sits on the seat with much speed during a normal operation, a false activation may occur. In order to prevent such false activation, the load at which the connecting portion starts moving rearward has to be set high. Accordingly, it is difficult to configure the structure in a manner that allows activation of the connecting portion easily at the time of a collision of vehicles.
In view of the above, there exists a need for a seatback for a vehicle which overcomes the above mentioned problems in the prior art. Specifically, there exists a need for a vehicle seatback that can mitigate impact to the occupant at the time of collision without causing an inconvenience during the normal operation. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It is an object of the present invention to provide a seatback for a vehicle that can mitigate impact to the occupant at the time of collision without causing an inconvenience during the normal operation.
The aforementioned object can be attained by providing a vehicle seat comprising a seat bottom, a seatback, at least two elastic supporting members, a displacement mechanism and a trigger mechanism. The seat bottom supports a buttock of an occupant. The seatback supports an upper body of the occupant. The elastic supporting members is disposed in a transverse direction within the seatback. The elastic supporting members includes a lower support member disposed to support a pelvis of the occupant and an upper support member disposed to support a back of the occupant. The displacement mechanism is disposed within the seatback and is coupled between the seatback and the upper support member to move the upper support member in a rearward direction relative to the seatback. The trigger mechanism is disposed within the seatback and is operatively coupled to the displacement mechanism at the lower support member to activate the displacement mechanism only upon receiving a rearward load greater than a predetermined value.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.